FIGS. 11 and 12 are an exploded perspective view and a perspective view conventional transformer 5001 disclosed in Japanese Patent Laid-Open Publication No. 2003-22917, respectively. Transformer 5001 includes closed-magnetic-circuit core 1, primary bobbin 3 assembled with core 1, two secondary bobbins 5 assembled with core 1, primary coil 2 wounded in coil groove 8 of primary bobbin 3, secondary coils 4 wounded in coil grooves 8 of two secondary bobbins 5 a primary coil terminal embedded in primary bobbin 3 and connected to one end of primary coil 2, low potential terminals 6A and 6B embedded in secondary bobbin 5 and connected to one end of secondary coil 4, and high potential terminals 7A and 7B connected to another end of secondary coil 4.
Closed-magnetic-circuit core 1 includes rear magnetic legs 9A and 9B having flat shapes are facing each other, two inner magnetic legs 10, two outer magnetic leg 11A, and two outer magnetic legs 11B. Inner magnetic legs 10, outer magnetic leg 11A, and outer magnetic legs 11B are connected to two rear magnetic legs 9A and 9B between rear magnetic legs 9A and 9B. Outer magnetic leg 11A has a rectangular column shape. Outer magnetic legs 11B have cylindrical column shapes. Primary bobbin 3 is assembled with outer magnetic legs 11A. Secondary bobbins 5 are combined with outer magnetic legs 11B, respectively. A gap is provided between inner magnetic leg 10 and rear magnetic leg 9A.
A straight discharge lamp is connected to low potential terminal 6A connected to one end of secondary coil 4, and connected to high potential terminal 7A connected to another end of secondary coil 4. Another straight discharge lamp is connected to low potential terminal 6B connected to one end of another secondary coil 4, and is connected to high potential terminal 7B connected to another end of another secondary coil 4. Transformer 5001 illuminates the two straight discharge lamps and is used as an inverter transformer for a back light of a light-transmittable display device, such as a liquid crystal display.
The display device has a screen having a large size, accordingly requiring two or more straight discharge lamps as its back light. If respective lighting timings of these straight discharge lamps are different from each other, a brightness variation may be caused on the screen of the liquid crystal display using these straight discharge lamps.
In general, there is a variation in properties, such as impedance of the discharge lamps and a stray capacitance of peripheral components. If one of the discharge lamps is turned on first due to the variation of the properties, a voltage output from secondary coil 4 connected to another discharge lamp may be lowered to a value lower than a voltage of secondary coil 4 connected to the discharge lamp which is turned on first. Accordingly, another discharge lamp which is connected to another secondary coil 4 may not be turned or may be turned on late.